Heat exchanger element



Dec. 24, 1935. A. J. BERG I HEAT EXCHANGER ELEMENT 2 Sheets-Sheet l INVENTOR Original Filed Aug. 6, 1926 BY I ATTORNEY Dec. 24, 1935. A. J. B-ERG 2,025,036

HEAT EXCHANGER ELEMENT Original Filed Aug. 6, 1926 2 Sheets-Sheet 2 //j N v 14.65950 X55196 INVENTOR ATTORNEY ing.

Patented Dec. 24, 1935 UNITED srArEs zpzsmt rarer OFFICE Divided and this application February 3, 1928, Serial No. 251,589

22 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) My invention relates to heat exchangers and more especially to heat exchanger elements, such for example as tubes, having heat-transferring fins or vanes thereon. The object of the invention is to provide afiimed heat exchanger element of improved construction.

Another object of my invention is to provide a finned heat exchanger element in which the fins are secured firmly upon the tube and ingood heat-conducting relation therewith without the use of fused metal, such for example, as solder, and without the creation or application of any heat such as would remove the natural or drawn temper of either the tube or the fin. Another object of my invention is to provide a heat exchanger element having fins thereon which are substantially perfectly smooth and. which therefore ofier the least resistance to the passage of air or' gas thereover.

Another object of the invention is to produce a heat exchanger element of this character which is of ru ged construction and which also can be manufactured comparatively easily and at relatively low cost, and which will enable the formed tube to be readily bent in any desired shape without the substantial distortion of either the tube or its Heretofore in cylinders of the finned type, it

has been customary to either cast the fin integral paratus and the production of brittle material.

The welding and brazing method is slow, and weakens the-tube and its fin, besides unduly increasing productioncosts, and is tedious and often fails to give a sufiiciently rigid and eilicient joint to allow a ready transference of heat.

My invention, however, insures a physical contact between the main body and the heat radiating fin at such a pressure as to provide a most efiicient heat'conducting joint and at the same time a mechanically strong joint superior to weld- Reference is to be had to the accompanying drawings forming a part of this specification in which like reference characters indicate correvsponding parts throughout the several views, and

or strip to tubing in the manufacture of my improved heat exchanger element;

Figs. 4 and 5 are respectively a side and an end view of a detail of this apparatus, namely the crimp wheel; 5

Figs. 6, 7, 8 and 9 are fragmentary sectional views illustrating the manner in which the edgewise-placed ribbon is secured to the surface of the tube; and J 7 Figs, 10 and 11 show an end and a side view respectively of a fragment of completed heat exchanger tube.

Figure 12 is a fragmentary sectional view illustrating the dishing of the strip 3 as the same is securedin its spiral form to the 15 Referring more particularly to Figs. 1, 2 and 3, Jnumeral l indicates one type of groove former consisting of a triple grooving cutter rigidly secured to tool body i by means of tap bolt 2 The function of the cutter will be described in detail later. Numeral 3 denotes the metal fin forming strip free to move in a direction parallel .to the tool body. The strip is guided in a vertical plane by passing it between flat metal plates l3 and II attached to the tool body by screws l5, plate 13 having a flat countersunk portion to accommodate the thickness of strip. a

Reference character 4 designates a lead wheel preferably consisting of two metallic disks, spaced apart approximately the thickness of the ribbon or strip. These disks are free to rotate upon a bearing passing transversely to the tool body to which it is attached bymeans' of thrust member H- and screw it. As shown in Fig. l, this bearing is not normal to the length of tool body I but is placed at an angle thereto for reasons to be stated.

The crimp wheel 5, shown in detail in Figs. 4

and 5, is made up of two rotating disks secured 40 together by means of screws l1, one of said disks having a bearingmember held within the tool body by thrust screw J2. The axis of rotation of the crimp-wheel is inclined, when considered inthe vertical plane, causing the wheel to tilt upwardly, as best seen in Fig. 1'. As shown in Fig. 4, I prefer to chamfer the two contacting surfaces of the crimp .wheel disks to such an angle' as will loosely accommodate a fin after being placed upon a tube. The tool body proper consists of wrought steel member 'l 'cut at one end to fit a standard tool post and tapered in thickness at the other end to an angle coincidingwith that defined by the Pbi=e between the lead wheel disks which in turn an arcuate-portion cut out at one end corresponding to the curvature of the tube or cylinder 2| and is square threaded as shown by dotted line I 8 to clear any burr raised in forming the grooves, as will be explained later. In addition to partially surrounding the tube member 6 is provided an inclined bearing surface for outterlasbeStshowninFlgB.

Rigid connection is' made between the tool body and member 8 by means of clamp screw 8 passing through slot 9.- The to'ol'body has an arcuate portion cut transversely to correspond with that in the back rest member, the combined arcs completing a circle having a diameter slightly larger than that of tube 2|.

At- I9, I have indicated oil holes for lubricating the bearing surfaces of the leadand crim wheels. I

I The manner of operation of my device is as folows: J

The tool body is rigidly fastened in the tool post of a standard lathe equipped with thread cutting gear. The tube or cylinder to be finned is placed between lathe centers in the usual manner. Upon the machine starting, the triple groove cutter is moved to'cut into the cylinder the reqiiired depth. This tool is of the stepped type,

' each successive cutter penetrating to a greater depth so that one e completely finishes the helical groove. The cutter may be of a shape to form agroove having parallel side walls as shown in Fig. 8, or'a groove having slightly divergent side walls as shown in Fig.6. The groove shown in. Fig. 8 is of greater width than the groove shown in- Fig. 6. The purposeof inc the width of the groove will later become apparent.

Also as will become apparent, the groove shown in'Flg. 6 may if desired. a i

As illustrated to advantage in Fig. 2 the metal ribbon 8 may be led from a suitable carrier such formed with parallel side walls as a spo'olor the like (not shown) and passed between the'guide plates," and I4. The strip may be extended into the peripheral groove of lead wheel 4, and with the tube 2| rotating in the proper direction, the operation of the appaproceed. With the cutters or groove formers I arranged to pro'videa groove such/as shown in-Flgfi 6, and'the'wheel 4' arranged so that its fin or strip receiving groove is in 'aline nient with the spiral groove formed by the meml,"theiwhe'el '4 operates to serve'two'purpoem, first. ,that of bending the strip 3 tothe contourofthe tube Ilwhenthe preceding portion said. that the bending operation oi' the strip occurs simultaneously with its insertion into the groovepreparedinthetube. Thebendin'gof' .the stripiato spiral form causes the inner edge thereof to thicken appreciably, which thickening tion is best illustrated in Figs. 6 and 'i. As shown in these figures the strip 3 is inserted into the groove in tube and as it is bent and as its inner edge is forced against thebottom of the groove, the edge is upset and thickened, forcing the strip into intimate, firm and efiicient thermal contact with the side walls of the groove. When certain materials of strip and tubes are used, the sida of the groove may be actually forced outward, as shown particularly in Fig. 7. The upsetting of the inner edge of the strip 3 forms an exceedingly tight joint between the tube and the fin. The union provided is in the form of a dovetail joint. The joint obviates any possibility of the tube releasing the fin, and permits heat to ,15

pass from the tube to the fin with substantially the same rapidity or efficiency as in the case when the fin is made integral with the tube. The joint between the tube and fin or strip secured by the operation heretofore described is clearly illus- 20 4 to the groove in the tube II the manner in which the inner edge of the strip or fin engages the side walls of the groove may be controlled. If the wheel 4 is inclined as shown in Fig. 2 the joint shownin Fig. 8 may be obtained.

In this operation, the inner edge of the fin is turned upon itself as illustrated. This is due to the reason that as the fin or strip 3 enters the groove, the inner edge of the strip engages with a side wall of the groove and turns uponitself.

It is also to be understood that the expansion in thickness of the metal about the inner edge of the strip is utilized in obtaining the joint shown in Fig. 8. This expansion takes place while the fin is being pressed into the groove and during the period the inner edge of the fin is 5 being turned upon itself. The stretching of the metal laying without the inner edge of the fin ,or strip during the bending thereof added to the upsetting of the inner edge of the strip produces a joint between the tube and fin of great strength and durability.

The crimping wheel 5 follows the operation of the lead wheel ,4. The wheel 5 straddles the fin and its peripheral edgesexert a pressure agaihst the metal of the tube lying adjacent to the-sides of the fin. The pressure of the wheel may be adjusted so that'sufiicient metal is depressed along the edges of the fin receiving groove of the tube to seal the outer side. walls of the groove against the adjacent walls of the fin as shown F to advantage ,in Fig.7.

Sufilcient pressure may be given wheel 5 to press themetal of the tube adjacent to the side willsofthefintotheextesitshowninl'lgl Inthislattercasethe portioliol-theilncontiguoiis with the outer edges 61 the groove is depressed and the metaiabout thewinner edge of thefinfurthei expanded. Thisaddedexpansion of the'metal about; the inner edge the fin I outwardly to s elbottom portion of thewalls of the tip receiving groove and produces a joint similarto that shown in 9. In this last mentioned method thejointbeplace during the time the edgeJs being tween-the fin and the tube, is strengthened.

the groove of tube, Th3 operaalso the joint prodacedhasahighheatconduct- 25 Such as f ing efficiency, the same as is the case with the joints shown in Figs. 7 and 8.

In Figs. 10 and 11, I have shown a section of a finned tube complete. At 20, I have indicated a series of prick-punch indentations equally spaced around the tube to constitute a securing means additional to that gained by knurling or plain rolling of the periphery of the crimping wheel 5 upon the tube or element on each of the opposite sides of the fin. The knurling 2 lb, or plain rolling being obtained respectively according to whether the periphery of wheel 5 be crimped or knurled in the one case or smooth in the other case. At least the peaks of the plurality of protrusions formed by the crimping or knurling 2|b extend beyond the inner or adjacent edge of the fin and further assist in theanchoring of the fin to the tube or element, as well as to increase the rate of heat exchange of the element adjacent the fin. The use of these indentations is purely optional.

The portion of the periphery of roller 4 in contact with a portion of the edge of strip-3, whose preceding portion has been secured to the rela tively revolving tube 2|, exerts substantial pressure upon strip 3 and between the contacting surfaces of strip 3 and tube 2|, as well as between the contacting surface of strip 3 with the periphery of roller 4. The extent of such pressure is dependent upon the width of strip 3 and the distance between the bottom of the cooperating grooves in tube 2| and roller 4, and said pressure is extensive enough to place strip 3 under a substantial stress, and the bottom of groove in roller 5continues such stress while the tops of the sides of said groove in roller 5 knurls strip 3 into said groove in tube 2| while strip 3 is still under said stress. Said stress tends to compress and thicken or curl the inner .edge of strip 3 within said groove, as heretofore described, which is also due in part to the tension on strip 3 of plates l3, l4 adjustable by screws l5.

The grooves in the peripheries-of rollers 4 and 5 are each tapered, Figure 4, the bottom narrowing to the normal thickness of strip 3 in orderto confine the outer edge of strip 3 in the spiral path fixed by the bottoms of said grooves in rollers 4 and 5 while the correspondingly spiral groove in tube 2| confines the inner edge of strip 3 in said spiral'path.

Said tension on strip 3 between the bottoms of said grooves, together with the width and thinness of metal strip 3 is such as to dish strip 3, the channel of such dishing extending lengthwise of strip 3 as it extends about tube 2| as shown at 3a in Figure 12, which, with the securement of strip 3 about tube 2| while strip 3 is under the aforesaid substantial tension, longitudinally and inwardly, enables a relatively thin strip 3 to be employed which, but for said tension and dish, would be frail and easily bendable. However said securement to tube 2| of strip 3 while under said tension affords very substantial strength to thin relatively wide strips 3 which affordsgreater heat conductive capacity away from the tube due to the said thinness of strips 3' and their increased number affordable thereby and to the intimate continuous bond between tube 2| and the strip 3.

The V-shaped grooves in rollers 4 and 5 limits greater than the normal volume of heat within tube 2| may thereby be conducted to strip 3 throughout its length and thereby causes said spiral strip 3 to receive from tube 2| a greater amount of heat than otherwise to radiate into 5 the atmosphere, while intermediate of said spiral areas of increased denseness, the areas of lesser denseness of the metal of tube 2| conducts only its normal amount of heat from within tube 2| to the atmosphere'in contact with the outer surface of such normal areas of tube 2|.-

The heat or cold, instead of being in or within member 2|, may be upon the outside thereof and in contact with the fins formed by strip 3 and with the outer surface of member 2| between said 15 fins and which said fins and intervening spaces constitute means for exchanging heat with each of said areas of greater and lesser heat conductive capacity of member 2|.

The marks 2| b, Figure 11, on opposite sides of 20 strip 3 when spirally wound upon and secured to tube 2| are relatively small indentations produced by the knurling surfaces of wheel 5 which straddles strip 3, and said indentations increase the area of said surface and its exposure to the 25 media in contact therewith and thus facilitates the heat interchange between said surface and media.

The pressure of rollers 4 and 5 upon the outer edge of strip 3, which causes'the thickening or 30 upsetting of the inner edge of strip 3 against the bottom as well as the side walls of the groove in tube 2|, in addition to increasing the thermal efficiency of the union between said strip and tube also increases the heat. exchange capacity of said 5 thickened or upset edge of strip 3.

My product is peculiarly adapted to, and readily facilitates, its being bent in any desirable shape, required in refrigeration and other apparatus without substantial distortion and liability 40 to rupture of either the element or its fin due to alternate spiral integral areas of difierent densities of the metal of the element.

The fin being spirally wound about the same under substantial longitudinal and inward 45 stresses and is secured to said element substantially throughout its spiral length while subjected to said stresses.

, While I have shown and described specific shapes of joints obtained by a definite relation 50 between the diameter of the lead and crimp' wheels with respect to that of the tube. in addition to the relative positions of the wheels and the pressure with which they operate either upon the strip or the metal adjacent the strip, the type 55 of joint may be modified to meet a given condition by changing the above relations. It is also apparent that the cutting of the groove may be.

r done by a tool separate and distinct from the of tube. This great increase in eificiency and the strip may not be wound edgewise and uprightly, at an angle of about 90 to the length of the tube. The same is furthermore due to the uniform thinness of the spaces between the fin convolutionsjto the high thermal conductive firm andcontinuous metal to metal non-fusion con-.

tact between the imbedded edge of the fin and the tube and to the area of greater thermalconductivity and increased density of metal of the tube in contact with the fln convolutions. But said thinness and width of fin strip may, with said heat exchanger emciency, be materially increased, and the stability and rigidity of the helical coiledfin substantially augmented, by the substantial longitudinal stress remaining in the fin strip after it is coiled helically about and secured to the tube. The strength and stress resistance of the tube and fin, as secured together in the finished product, are furthermore increased by retaining all of their original characteristics.

Said advantages also directly result in material cost and weight savings for the-diiferent required capacities of heat exchange. In many installations the saving in weight attained by my invention is of vital importance, typically in aircraft and in ships. 1

This application is a division of my copending application Serial No. 127,692, filed August 6, 1926, patented May 1, 1928, numbered 1,668,534.

The invention herein described may be manufactured and used by or for the Government of the United States for governmental p without the payment to me of any royalty thereon or therefor.

What I claim as new; and desire to secure by Letters Patent of the United States is:

1. A heat exchanger element having very large heat exchanging surfaces per unit of length and weight comprising a metallic small dia'metered relatively long tube whose bore is open and adapted to receive a flowing fluid whose temperature is desired to be changed by conduction through the wall of the tube' whose exterior is provided with a very thin and wide continuous integral ribbon of sheet metal of original uniform thickness helically extending edgewise thereabout, at

least portions of adjacent surfaces of the ribbon and of the tube extending the one beyond the other for securing them together, the metal of the fln being so wide and thin that it may not uniformly edgewise wind upright about the small diameter of the tube in the absence of lateral support at least at the point 'where it bends edgewise about the tube. there being a uniform relatively narrow. space between the ribbon helices forming the fin, metal of the tube being secured in firm and continuous contact with and substantially integrally connected without molten metal fusion to all parts of the embedded portion of the inner edge of the ribbon comprising the helical fin about the tube; the metal of the secured fin being and continuing under substantial longitudinal stress and having all of the characteristics of the sheet metal of which it was formed with its-resistance to'deformation increased by said longitudinal stress present in the metal of the fin and by said securement to the tube; the metal of the tube retaining all of its normal conductlon'characteristics and the tube having its rejsistance to deformation and its heat exchange eflicienc'y to and from the fin increased by an area of increased density of its metal extending helically about the tube in thermal lateral contact with the fin; the outer surfaces of the tube and helical fin being adapted to be contacted by a fiuid whose temperature is desired to be changed by conduction through the fin and the wall of j the tube; whereby the stability, durability and efliciency of the exchanger element is materially increased and its weight and required space substantially reduced.

2. A heat exchanger element having very large heat exchanging surfaces per unit of length'and weight comprising a metallic tube whose bore is 5 open and adapted to receive a flowing fluid whose temperature is desired to be changed by conduction through the wall of the tube whose exterior is provided with a very thin and wide ribbon of 1 sheet metal of original uniform thickness forming a fin helically extending thereabout edgewise substantially from the tube with the inner edge of the fin secured to and in thermal contact with the tube, said fin extending from the tube outward in a symmetrical arc coextensive 15 with the width of the fin and said are extending helically throughout the convolutions of the tube for increasing the thinness of the fin metal and the number of fin convolutions per unit of tube length and increasing the strength and freedom 20 from deformation of the fin and for increasing the width of the fin employable on a given tube, and the outer surfaces of the tube and helical arched fin being adapted to be contacted by a fluid whose temperature is desired to be changed 25 by conduction through the wall of the tube and to the" fin.

3. The heat exchanger element of claim 1 which is further provided with a. slightly increased 1 thickness of the inner embedded edge "or the fin, 3i)

and the longitudinal tension of the secured fin convolutions being greater at the cuter than at the inner edge of the fin convolutions.

4. The heat exchanger elementof claim 1 which is further provided with a roughened portion of 5 varying diameter of the outer surface of the tube adjacent each fin, convolution. L

5. A heat exchanger element comprising a metallic cylindrical member having a thin and wide continuous sheet metal fin of uniform thick- 0 ness extending helically thereabout with its. in-

ne; edge securedthereto, said fin having a series I of lateral depressions formed therein near the outer surface of the member. 6. A heat exchanger element having very large 45 heat exchanging surfaces per unit of length and weight comprising a metallic small diametered relatively long tube whose bore is open and adapted to receive a flowing fluid whose temperature is desired to be changed by conduction through the wall of the tube whose exterior is provided with a very thin and wide continuous integral ribbon of sheetmetal of original uniform thickness forming a fin helically extending edgewise thereabout, at least portions of the tube and the ribbon extending the one beyond the other for securing them together in firm thermal contact with and substantially integrally connected without molten metal fusion, said fin extending from the tube outward in a symmetrical arc coextens'lve with the width of .thefin, said are extending helically throughout the convolutions of the fin; the outer surfaces of the tube and helical arched fin being adapted to be contacted by a separate fluid whose temperature is desired tobe changed by conduction through the wall of thetube and to the fin; the metal of the secured fin being and continuing under longitudinal stress and having and from the fin increased by an area of increased density of its metal extending helically about the tube in thermal lateral contact with the fin; whereby thinner metal for, and a greater number of fins per unit length of tube may be employed and far greater heat exchange efiiciency obtained and maintained with less liability to accidental deformation of tube as well as fin.

'7. A heat exchanger element having very large heat exchanging surfaces per unit of length and weight, comprising a metallic small diametered relatively long cylindrical member whose exterior is provided with a very thin and wide continuous integral fiat ribbon of sheet metal of original uniform thickness helically extending edgewise thereabout and whose inner edge is in contact with the metal of the member, the metal ribbon being so wide and thin that it may not uniformly edgewise wind upright about the relatively small diameter of the .member in the absence of lateral support at least at the progressive point where the ribbon bends edgewise helically about the member, there being a uniform relatively narrow space between the ribbon helices, and metal of the member being in contact with small portions of the opposite sides of the ribbon helices and securing the ribbon helices to the member.

8. A heat exchanger element having very large heat exchanging surfaces per unit of length and weight, comprising a metallic small diametered relatively long cylindrical member whose exterior is provided with a very thin and wide continuous integral flat ribbon of sheet metal of original uniform thickness helically extending edgewise thereabout and whose inner edge is in contact with the metal of the member, the metal ribbon being so wide and thin that it may not uniformly edgewise wind upright about the relatively small diameter of the member in the absence of lateral support at least at the progressive point where the ribbon bends edgewise helically about the member, there being a uniform relatively narrow space between the ribbon helices, and roughened portions of the member being in contact with small portions of the opposite sides of the ribbon helices and securing the ribbon helices to the member.

9. A heat exchanger element having very large heat exchanging surfaces per unit of length and weight, comprising a metallic small diametered relatively long cylindrical member whose exterior is provided with a very thin and wide continuous integral ribbon of sheet metal 'of original uniform thickness helically extending edgewise thereabout and whose inner edge is in contact with the metal of the member, the metal ribbon being so wide and thin that it may not uniformly edgewise wind upright about the relatively small diameter of the member in the absence of lateral support at least at the progressive point where the ribbon bends edgewise helically about the member, there being a uniform relatively narrow space between the ribbon helices, the surface of the element being knurled on opposite sides'of the helically extending ribbon of sheet metal.

10. A finned element having a thin wide continuous metallic fin tightly extending edgewise along the surface of the element, and protrusions on the surface of the element on opposite sides of the fin with at least the peaks of the protrusions being outward from the inner edge and in contact with the sides of the fin.

11. A finned element having a thin, wide, flat, continuous metallic fin of original uniform thinness tightly extending edgewise along the surface of the element, and a plurality of knurl marks on the element forming protrusions extending on opposite sides of the fin with at least the peaks of the protrusions being outward from the inner edge and in contact with the sides of 5 the fin.

12. A heat exchangenelement having very large heat exchanging surfaces per unit of length and weight, comprising a metallic member whose exterior is provided with at least one very thin, wide, flat, continuous integral ribbon of sheet metal of original uniform thickness extending edgewise at short intervals from the surface of the element and the inner edge of the ribbon being in contact with and secured to metal of the element, without molten metal fusion, the metal of the secured fin being and continuing under longitudinal stress which tends to resist accidental deformation of the fin.

13. The heat exchanger element of claim 12 further characterized by the surface of the element being knurled on opposite sides of the fin.

14. The heat exchanger element of claim. 12

further characterized by the surface of the element on opposite sides of the fin having protrusions with at least the peaks of the protrusions being outward from the inner edge and in contact with the sides of the fin.

15. A finned element having a thin, wide, flat, continuous sheet metal finof original uniform thinness tightly extending edgewise along the surface of the element with its edge in thermal contactwith and secured to metal of the element, the fin being arched transversely to the length of the fin for resisting accidental deformation of the thin fin.

16. A finned element having a thin, wide, fiat, continuous sheet metal fin of original uniform thinness extending edgewise helically about the element, and having an edge secured to the element under a maintained longitudinal stress of the fin and which stress is greater at the cuter than the inner edge of the fin.

17. A heat exchanger comprising a hollow element having at least a portion of its surface provided with a plurality of separated, substantially parallel portions of a groove, a thin stressed metal ribbon having an edge portion thereof extending into said groove portions, forming heat exchanging fins projecting at a substantial angle from said portion of the surface of the element, and metal of the element adjacent said edge portion being in direct binding contact with lateral sur faces of said edge portion.

18. The heat exchanger of claim 17 characterized by the metal ribbon being under longitudinal stress maintained by said binding contact.

19. A heat exchanger comprising a metallic member substantially surrounded at spaced intervals by portions of relatively thin metal extending throughout at least its major extent at a substantial angle to the member and having a portion engaging a surface of the member, and said member Having a knurled surface adjacent the thin metal. 05

20. The heat exchanger of claim 19 characterized by the knurled surface being on opposite sides of the thin metal.

21. A heat exchanger comprising a metallic member having relatively thin metal extending 7 about at least a substantial portion of and at a substantial angle to said member, and having a portion engaging a surface of said member, and said member having a knurled surface on opposite sides of the thin metal with at least the peaks of g,

said knurled surfaces being outward from said engaging surface, and contacting lateral portions of said thin metal.

22. A heat exchanger comprising a metallic member having a thin, wide strip of stressed metal extending, at short intervals, at a-substantial angle to said member; said strip being under longitudinal stress and having a thickened inner edge secured to the member by portions of metal of the member extending outward from the inner edge and in contact with a portion of the lateral 

